<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <style type="text/css" media="screen">
            /* 按钮loading */
a[class*=-btn].loading, 
label[class*=-btn].loading {
    position: relative;
}
a[class*=-btn].loading::first-line, 
label[class*=-btn].loading::first-line {
    color: transparent;
}
a[class*=-btn].loading::before, 
label[class*=-btn].loading::before {
    width: 4px; height: 4px;
    margin: auto;
    content: '';
    -webkit-animation: spinZoom 1s steps(8) infinite;
    animation: spinZoom 1s steps(8) infinite;
    border-radius: 100%;
    box-shadow: 0 -10px 0 1px currentColor, 10px 0 currentColor, 0 10px currentColor, -10px 0 currentColor, -7px -7px 0 .5px currentColor, 7px -7px 0 1.5px currentColor, 7px 7px currentColor, -7px 7px currentColor;
    /* center */
    position: absolute;
    top: 0; right: 0; bottom: 0; left: 0;
}
/* loading动画 */
@-webkit-keyframes spinZoom {
    0% {
        -webkit-transform: scale(.75) rotate(0);
    }
    100% {
        -webkit-transform: scale(.75) rotate(360deg);
    }
}
@keyframes spinZoom {
    0% {
        transform: scale(.75) rotate(0);
    }
    100% {
        transform: scale(.75) rotate(360deg);
    }
}
        </style>
    </head>
    <body>
        <a class="-btn loading"></a>
    <script type="text/javascript">
        var a={
            b:function(){
                console.log(this)
            },
            c:()=>{
                console.log(this)
            }
        }

        a.b()
        a.c()
        console.log(a.c.prototype)
        //箭头函数 没有prototype 没有this作用域 不存在变量提升 不能用来构造函数
        //
        //
        console.log(bbb)
        var bbb=1
    </script>
    </body>
</html>